As world population continues to grow, natural resources are under increasing pressure, threatening public health and social and economic development, warns a new report from the Johns Hopkins School of Public Health.

"As we humans exploit nature to meet present needs, are we destroying resources needed for the future?" ask Don Hinrichsen and Bryant Robey, co-authors of the latest issue of Population Reports, Population and the Environment: The Global Challenge, published by the Johns Hopkins Population Information Program.

"Most developed economies currently consume resources much faster than they can regenerate. Most developing countries with rapid population growth face the urgent need to improve living standards" but risk irreparable harm to natural resources on which they depend, according to the report.

"Water shortages, soil exhaustion, loss of forests, air and water pollution, and degradation of coastlines afflict many areas," write the authors. "Without practicing sustainable development, humanity faces a deteriorating environment and may even invite ecological disaster," they note.

Sustainable development requires slower population growth. While the rate of population growth has slowed over the past few decades, the absolute number of people continues to increase by about 1 billion every 13 years, and the environment continues to deteriorate. "Can we assume that life on earth as we know it can continue no matter what the environmental conditions?" ask the authors.

Over the past 10 years, environmental conditions generally have either failed to improve or appear to be getting worse, a review of the evidence finds. For the future, how people protect or abuse the environment could largely determine whether living standards improve or deteriorate, according to the authors.

Despite international concern about the environment since the 1992 Rio de Janeiro "Earth Summit," nearly every environmental sector is still cause for concern:

o Unclean water, along with poor sanitation, kills over 12 million people a year. Air pollution kills 3 million more.

o In 64 of 105 developing countries, population has grown faster than food supplies. Overcultivation, largely due to population pressures, has degraded some 2 billion hectares of arable land -- an area the size of Canada and the United States.

o By 2025, with world population projected to be at 8 billion, 48 countries containing 3 billion people will face chronic water shortages. In 25 years, humankind could be using over 90 percent of all available freshwater, leaving just 10 percent for the rest of the world's plants and animals.

o Half of all coastline ecosystems are now under pressure because of high population densities and development. About half the world's population occupies a coastal strip 200 kilometers wide -- just 10 percent of the world's land surface.

o Over the past 50 years nearly half of the world's original forest cover has been lost. Current demand for forest products may exceed the limits of sustainable consumption by 25 percent.

o Since 1950, according to one estimate, some 600,000 plant and animal species have disappeared, and currently nearly 40,000 more are threatened. This is the fastest rate of extinction since the dinosaurs disappeared.

o Over the past 40 years ocean surfaces have warmed an average of over half a degree Celsius, mainly as a result of carbon emissions from fossil fuel use and from burning of forests. Global warming could raise the sea level by 1 to 3 meters as polar ice sheets melt, flooding low-lying coastal areas and displacing millions of people. Global warming also could result in droughts and disrupt agriculture.

The report urges governments and policymakers to take immediate steps toward implementing sustainable development. Sustainable development means raising current living standards without destroying the resource base required to meet future needs.

In effect, the world needs to live off its "ecological interest" rather than using up its "ecological capital," the authors write.

Steps toward sustainable development include using energy more efficiently; managing cities better; phasing out subsidies that encourage waste; managing water resources and protecting freshwater sources; harvesting forest products rather than destroying forests; preserving arable land and increasing food production -- a second Green Revolution; managing coastal zones and ocean fisheries; protecting biodiversity hotspots; and adopting a climate change convention among nations.

Stabilizing population through good quality family planning services "would buy time to protect natural resources," according to the report. It would also provide opportunities for women and families to raise their living standards.

The authors note that the number of people in developing countries who want family planning services has risen, but annual global spending on family planning programs is less than half the US$17 billion agreed to for 2000 at the UN International Conference on Population and Development in Cairo in 1994. Developed-country annual commitments total just $2 billion -- less than half the US$5.7 billion they promised to donate at Cairo.

In the balance is whether the world's population could eventually stabilize at 9 billion or less, or whether it will grow to 11 billion and even beyond. "Just when it stabilizes will have a powerful effect on living standards and the global environment," write the authors.

Don Hinrichsen is a senior consultant with the United Nations Population Fund (UNFPA). Bryant Robey is editor of Population Reports, an international review journal of important issues in population, family planning and related matters.

It is published four times a year in four languages by the Population Information Program at the Johns Hopkins Center for Communication Programs for more than 170,000 family planning and other health professionals worldwide, with support from the US Agency for International Development (USAID). USAID administers the US foreign assistance program, providing economic and humanitarian assistance in more than 80 countries worldwide.